What does bilateral innervation of cranial nerves mean?

Answer 1

Cranial nerves that have a motor function tend to be bilaterally innervated. In other words, the right accessory nerve (XI) receives input from both the right and the left motor cortex. The same goes for the left accessory nerve.

This is a handy advantage in strokes, since upper motor neurone lesions must therefore be bilateral in order to cause a deficit.

The one major exception to this rule is the facial nerve (VII). Only the forehead muscles are bilaterally innervated, so even a unilateral upper motor neurone lesion can cause mouth drooping, etc. However, this can still often be differentiated from a lower motor neurone lesion, which will not spare the forehead.

Answer 2

Bilateral innervation of cranial nerves refers to the fact that each cranial nerve receives input from both the right and left sides of the brain. This setup ensures redundancy and helps maintain function in case one side of the brain or one cranial nerve is damaged. It is a common feature of important cranial nerves that are crucial for functions like vision, eye movement, and facial expression.